Saturable absorber component and method for production of a saturable absorber component

ABSTRACT

A saturable absorber component including an absorbent material located between a front mirror and a rear mirror, and a method for manufacturing a saturable absorber component. The rear mirror is a metallic buried mirror fixed by a welding joint on a heat conductive substrate. The saturable absorber can be applied to the field of high-rate optical transmission.

TECHNICAL FIELD AND PRIOR ART

The invention relates to a saturable absorber component for theprocessing of digital optical signals as well as a method formanufacturing a saturable absorber component for the processing ofdigital optical signals.

The component according to the invention has particularly advantageousapplications in the field of high-rate optical transmission (all-opticalsignal regeneration for transatlantic communication, modulation contrastamplification, wavelength conversion, temporal demultiplexing opticalsampling, etc.).

Telecommunications and information technologies are currently booming.This growth in the exchange of information requires greater and greatertransmission capacities.

In the case of optical signal transmission, the processing ofinformation is done after converting an optical signal into anelectrical signal. This conversion operation limits the processingcapacities of the communication networks. It is thus necessary toincrease the complexity of these networks in order to increase thequantity of processed information. To avoid this increase in complexity,it is indispensable to develop components capable of processing theoptical signal in an “all-optical” manner, that meaning without havingto convert the optical signal into an electrical signal.

Among the all-optical components the saturable absorber components areknown. Generally speaking, a saturable absorber component has thefollowing properties:

-   -   a non-linear characteristic according to the amplitude or the        signal phase (this property can be expressed, for example, by a        threshold transfer function);    -   a response time compatible with the rate of information, that        meaning less than the bit time (inverse of the rate);    -   a threshold power of the transfer function compatible with the        signal strength.

The functioning of a saturable absorber component is based on theabsorption saturation phenomenon of semiconductor materials. Thevariation of the absorption coefficient α of a semiconductor materialaccording to the intensity I of the incident signal that goes through itis represented in FIG. 1. The low intensity signals undergo theintrinsic absorption of the material and are consequently absorbed. Onthe other hand, high intensity signals reduce the semiconductor materialabsorption to a substantially nil value. This is the absorptionsaturation phenomenon. The high intensity signals are then transmittedwithout being absorbed.

The transfer function of T of a saturable absorbent material accordingto the intensity I of the incident signal is represented in FIG. 2. Thetransfer function of T is a non-linear function of the intensity I. Thematerial is opaque (T=T_(min)) at low intensity levels of the incidentsignal, for example the noise levels, and practically transparent(T=T_(max)) at high intensity levels, for example the “useful” signallevels. This defines the commutation contrast T_(max)/T_(min).

In order to reinforce the non-linear effect and the commutationcontrast, the saturable absorbent material can be placed in anasymmetric Fabry-Pérot cavity resonating to the operating wavelength.The cavity comprises two mirrors M1 and M2 of different reflectivitiesRb and Rf separated by a distance L. Such a cavity is represented inFIG. 3. After several round tours of the cavity, a standing wave systemis established with intensity nodes N and antinodes V. The couplingbetween the absorbent material and the incident light is thus reinforcedon one hand by the multiple round tours, and on the other hand byplacing the absorbent material at the antinodes of the standing wave.

A cancellation of the response of the component at weak signal rate, forexample noise, can be obtained by creating destructive interferencebetween the different beams reflected by the cavity. This cancellationis made via the following impedance adaptation condition:R _(f) =R _(b) .e ^(−2 αo L)  (1), where

-   -   Rfb is the reflectivity of the front mirror,    -   Rb is the reflectivity of the rear mirror,    -   αo is the intrinsic absorption of the material, and    -   L is the absorber thickness in the cavity.

Different functions can be implemented using a saturable absorbercavity. A first function is the modulation contrast amplification in thecase where only one signal is sent onto the cavity. Another functionrelates to the control of the optical door in the case where severalsignals are sent onto the cavity (a strong signal thus serves as acontrol signal so as to allow the transmission of low amplitudesignals).

An advantageous characteristic of the saturable absorber cavities isthat this type of component does not have any electrodes. This allowsfor extreme miniaturisation, a minimal dissipation of heat, and a veryeasy implementation as it is not necessary to envisage an electricalsupply. These advantages are particularly beneficial in the case wherewe wish to handle several canals of different wavelengths, as thesedifferent canals can thus be handled in zones neighbouring a singlecavity, with a space between the canals solely limited by the focusingconditions of the incident beams, whose diameter is typically about afew microns.

The creating of the impedance adaptation condition (see equation (1)) isindispensable in order to obtain optimal operating (high commutationcontrast). A tolerance study on this condition shows that its creationis all the easier when the cavity is highly asymmetric (Rf greatlyinferior to Rb). A high absorption is thus necessary in order to respectthis condition. This results in a high absorbed power which has to beevacuated to avoid deteriorating the performance of the component.

A saturable absorber cavity according to the known art is represented inFIG. 4. This cavity is divulged in the document entitled“Low-temperature-grown-surface-reflexion all-optical switch (LOTOS)” byRyo Takahashi, Optical and Quantum Electronics 33: 999-1017, 2001.

The cavity, highly asymmetric, comprises a front mirror 1 of very lowreflectivity (typically of about 1%), an absorbent material 2 made ofquantum wells constrained on a thickness of 4 μm, a phase control layer3 (InAlAs/InP layer) and a high reflectivity rear metallic mirror ingold (Au) 4 (typically greater than 95%). The low reflectivity mirror 1is covered in a growth substrate 5 on which is placed an anti-reflexionlayer 6.

The growth of semiconductor layers is done at low temperature. Thedoping of the quantum wells is performed at the same time as theirgrowth. High dosages of doping are necessary in order to reduce theresponse time. Each of these techniques. (low-temperature growth anddoping) deteriorate the non-linear properties of the absorbent material.

An incident light wave I1 which pierced the growth substrate 5 is partlyreflected by the front mirror 1 in the form of a wave 01. The wavetransmitted by the front mirror 1 performs a round tour in the cavity bybeing reflected by the rear mirror 4 in the form of a wave 02. Duringthis round tour in the cavity, the wave 02 is partly absorbed by theabsorbent material 2, then it is transmitted once again almost totallyby the front mirror 1. To obtain the destructive interference (minimumof the reflectivity) the two waves must be equal in amplitude andopposite in phase.

This cavity has several inconveniences among which we can cite:

-   -   the means of manufacturing which does not allow any control of        the cavity parameters (a high tolerance design is thus        indispensable, hence the choice of a highly asymmetric cavity        (R_(f)<<R_(b))),    -   a high value of power absorbed by the absorbent material due to        the relatively significant thickness of the material (4 μm), so        as to create the impedance adaptation condition (1);    -   a poor evacuation of the absorbed power due to the fact that the        rear mirror is in direct contact with the air which is a very        poor heat conductor;    -   a poor non-linear characteristic of the transfer curve of the        absorbent material due to the necessary high dosages of doping        as well as to the low-temperature growth;    -   an impossibility of controlling the parameters which control the        regulating of the component speed due to the fact that the        doping of the quantum wells is performed during the growth of        the wells;    -   an obligation to use a transparent growth substrate due to the        fact that the light must pass through the latter through its        entire thickness before reaching the cavity.

Furthermore, as previously mentioned, destructive interference must becarried out between the signal that is reflected by the front mirror andthe signal which, reflected by the rear mirror, passed through theentire structure. This destructive interference is created by settingthe thickness of the phase control layer, before the depositing of themetallic mirror. Yet, the metallic mirror considerably phase shifts thelight that it reflects. It follows that the subsequent depositing of themetallic mirror has a considerable risk of substantially modifying thestate of the interference. The performance of the component can prove tobe highly deteriorated.

The invention does not have these inconveniences.

Presentation of the Invention

Indeed the invention relates to a saturable absorber componentcomprising an absorbent material located between a front mirror and arear mirror. The rear mirror is a buried mirror fixed via a weldingjoint on a heat conductive substrate.

The invention also relates to a method for manufacturing a saturableabsorber component comprising an absorbent material located between afront mirror and a rear mirror. The method comprises:

-   -   the creating of a first structure via the depositing of a first        metallic layer on a heat conductive substrate;    -   the creating of a second structure comprising, on a growth        substrate, the absorbent material and a second metallic layer;    -   the bringing together of the first and second metallic layers;        and    -   the soldering via solid-liquid interdiffusion of the first and        second metallic layers.

The component according to the invention advantageously ensures a verygood evacuation of the absorbed power.

The method for manufacturing the component according to the inventionadvantageously allows to control the cavity parameters. Aninsignificantly thick absorbent material can thus be inserted in acavity with a highly reflective front mirror. This greatly reduces theabsorbed power and the heat effects.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages will appear upon reading apreferred embodiment of the invention made in reference to the annexedfigures among which:

FIG. 1 represents the variation of the absorption coefficient α of asemiconductor material according to the intensity I of an incidentsignal which passes through it;

FIG. 2 represents the transfer function of a saturable absorbentmaterial according to the intensity I of the incident signal whichpasses through it;

FIG. 3 represents a circuit diagram of a saturable absorber cavity;

FIG. 4 represents a saturable absorber cavity according to the priorart;

FIG. 5 represents a saturable absorber cavity according to theinvention;

FIG. 6 represents a first stage of manufacturing a saturable absorbercavity according to the first embodiment of the invention;

FIG. 7 represents a second stage of manufacturing a saturable absorbercavity according to the first embodiment of the invention;

FIG. 8 represents a third stage of manufacturing a saturable absorbercavity according to the first embodiment of the invention;

FIG. 9 represents a fourth stage of manufacturing a saturable absorbercavity according to the first embodiment of the invention;

FIG. 10 represents a fifth stage of manufacturing a saturable absorbercavity according to the first embodiment of the invention;

FIG. 11 represents a sixth stage of manufacturing a saturable absorbercavity according to the first embodiment of the invention;

FIG. 12 represents spectral characterisation curves of the saturableabsorber cavity according to the first embodiment of the invention;

FIG. 13 represents spectral response curves of the saturable absorbercavity according to the first embodiment of the invention;

FIG. 14 represents a first stage of manufacturing a saturable absorbercavity according to the second embodiment of the invention;

FIG. 15 represents a second stage of manufacturing a saturable absorbercavity according to the second embodiment of the invention;

FIG. 16 represents a third stage of manufacturing a saturable absorbercavity according to the second embodiment of the invention;

FIG. 17 represents a fourth stage of manufacturing a saturable absorbercavity according to the second embodiment of the invention;

FIG. 18 represents a non-linear transfer curve of a saturable absorbercomponent according to the invention;

FIG. 19 represents a temporal response curve of a saturable absorbercomponent according to the invention;

In all the figures the same references designate the same elements.

DETAILED DESCRIPTION OF THE MEANS OF IMPLEMENTING THE INVENTION

FIGS. 1, 2, 3 and 4 were previously described, it is therefore pointlessgoing over them again.

FIG. 5 represents a saturable absorber cavity according to theinvention. The cavity comprises:

-   -   a front mirror 7 (dielectric deposit or semiconductor mirror);    -   a first non-absorbent phase layer 8;    -   an absorbent structure 9 composed of quantum wells and barriers        separating the quantum wells (this absorbent structure can also        be composed of a solid semiconductor layer or by a structure        composed of quantum boxes);    -   a second non-absorbent phase layer 10;    -   a rear mirror 11;    -   a welding joint 12; and    -   a substrate 13 chosen so as to be a very good heat conductor.

Preferably, a diffusion barrier (not represented in the figure) islocated between the soldered joint 12 and the mirror 11.

The non-linear functioning of the component is obtained thanks to theexcitonic absorption saturation of the absorbent material. This effectis reinforced by an adaptation of the impedance of the asymmetricmicro-cavity formed by the front mirror 7, the absorbent medium 9 andthe rear mirror 11. The thickness of the absorbent layer 9 is preferablychosen of sufficiently low value (for example 100 nm) in order to allowa lowering of the energetic commutation threshold. The rear metallicmirror 11 is fixed to a very good heat conducting substrate 13 whichadvantageously ensures a very good evacuation of the absorbed power.Very good dynamic performance of the component is obtained thanks to thepresence of defects d created in the absorbent medium via ionirradiation and without any deterioration of the excitonic absorption.

It is thus necessary to choose a composition of materials that has goodabsorption saturation properties at the operating wavelength. Theabsorption saturation properties depend on the energy bands of thematerial. Preferably, the absorbent material is made using quantumwells. The composition of the quantum wells and the barriers whichseparate the quantum wells is thus adjusted in order to have asignificant excitonic absorption more particularly at the operatingwavelength.

A method for manufacturing the component according to the preferredembodiment of the invention will now be described.

FIG. 6 represents a first stage of manufacturing the component accordingto the first embodiment of the invention. The first stage is a growthstage of semiconductive layers on a growth substrate 15, for example anInP substrate. The semiconductive layers that are grown on the substrate15 are successively:

-   -   a barrier layer 14, for example an InGaAsP layer with a        thickness of 250 nm;    -   a first phase layer 8, for example an InP layer with a thickness        of 250 nm;    -   a unit 9 composed of the quantum wells and the barriers        separating the quantum wells, this unit being elaborated so as        to have the desired excitonic absorption properties at the        operating wavelength, for example 1.55 μm;    -   a second phase layer 10, for example an InP layer with a        thickness of 75 nm.

The number of quantum wells can be, for example, equal to 3, eachquantum well having a thickness of 9 nm and each separation barrierbetween the quantum wells having a thickness of 7 nm. This smallabsorbent thickness advantageously allows to reduce the heat effects andhave saturation power compatible with the available power at high rate.

The growth of semiconductive layers on the substrate 15 is carried out,for example, via MOVPE epitaxy (“Metal Organic Vapor Phase Epitaxy”). Amesh between the crystalline networks of the layers and the substratemust be respected. It is for this reason that the growth of layers isdone on an InP substrate and not, for example, on a silicon substrate(Si). The composition of the barrier layer 14 is adjusted so as toobtain an absorption band located, for example, around 1.41 μm and thethicknesses of the quantum wells and the barriers between the quantumwells are thus adjusted so as to obtain a significant excitonicabsorption around 1.55 μm.

The material growth stage on the growth substrate 15 is followed by anion irradiation stage such as is represented in FIG. 7.

Ions, for example Ni⁺⁶ ions, are sent onto the second phase layer 10.Hence they go through the structure composed of successive layers 10, 9,8 and 14 to end their travel in the growth substrate 15. During theirtravel, the ions create crystalline defects d in the absorbent material.The presence of defects in the absorbent material advantageously allowto accelerate the absorption relaxation process without deterioratingthe properties of the latter. Indeed, the defects play the role ofefficient capture centres for hole-electron pairs. The irradiationenergy is adjusted so that the ions go through the entire structure andend their travel in the growth substrate. The latter will then beremoved so as to avoid any residual absorption of ions.

The reduction in the time of absorption relaxation is directly linked tothe dosage of irradiation, that meaning to the number of ions persurface unit. This technique advantageously allows to adjust theresponse time of the component after the epitaxial growth stage of thesemiconductive layers. Response times inferior to a picosecond can beobtained without deteriorating the excitonic absorption. The ionsirradiation dosage of Ni⁺⁶ can, for example, be equal to 2.10¹¹ ions percm², which results in a component whose response time is substantiallyequal to 6 ps. The energy of the ions can be equal to 11 MeV, whichinduces a stopping distance substantially equal to 2 μm. The ions thusgo through the entire structure and land in the substrate (which will beremoved later on), all residual absorption is thus avoided.

The depositing of the rear mirror 11 and of a set of metallic layersfollows the irradiation stage, as is represented in FIG. 8.

The rear mirror 11 is deposited on the second phase layer 10. Thedepositing is carried out under vacuum conditions, that meaning, forexample, at a pressure substantially equal to 10⁻⁷ Torr. The materialused to make the mirror is a metal chosen for its good optical andthermal qualities, that meaning to have a high heat reflectivity andconductivity. A deposit of silver (Ag) or gold (Au) properly respectsthese two conditions. By way of non-restrictive illustration, a silvermirror with a thickness of 300 nm can be formed on the second phaselayer, after deoxidation of the surface of this second layer viachemical aggression based on hydrochloric acid (HCL) diluted to 10%. Thereflectivity of the rear mirror is thus equal to approximately 95%.

A set of metallic layers successively composed of a diffusion barrier, alayer of gold and a layer of indium are deposited on the rear mirror 11.Only the layer of indium 16 is represented in FIG. 8. The diffusionbarrier can be, for example, a layer of titanium (Ti) with a thicknessof 120 nm. The thickness of the layer of gold can be 300 nm and thethickness of the layer of indium can be 1200 nm. The ratio of thedeposited layers of gold and indium gives the gold/indium bilayer thecomposition of 60.2% in weight in indium.

On its side, a host substrate 13, for example a silicon substrate, iscovered in a layer of gold 17, as is represented in FIG. 9. The layer ofgold is, for example, a layer with a thickness of 300 nm. Prior to thedepositing of the layer of gold 17, a thin bonding layer of titanium(Ti) with a thickness of 20 nm can possibly be deposited on the hostsubstrate 13.

The structure such as is represented in FIG. 8 is thus brought intocontact with the structure such as is represented in FIG. 9. Thebringing together of the two structures is done, for example, in aclamping device under controlled pressure of approximately 6 bars. Asrepresented in FIG. 10, it is the layers 16 and 17 which are broughtinto contact one with the other so as to allow, in the conditionsdetailed below, the creation of a solder via solid-liquid interdiffusionmore commonly known under the solder appellation SLID (Solid-LiquidInterdiffusion). The process of fixing via SLID is described in thearticle entitled “Semiconductor Joining by the Solid-LiquidInterdiffusion (SLID) Process” by Leonard Bernstein, Journal of theElectrochemical Society, P. 1282-1288, December 1966) and in the articleentitled “Au—In Bonding Below the Eutectic Temperature” by Chin C., ChenY. and Goran Matijasevic, IEEE Transactions on Components, Hybrids, andManufacturing Technology, vol. 16, No. 3, May 1993, p. 311-316.

The principle of SLID solder is based on the presence, in the phasediagrams of some intermetallic binary systems, of a solidus jumpallowing to obtain, at low temperature (approximately 200° C., inferiorto the eutectic temperature), solders whose melting point exceeds twicethe temperature of the process (400° C.-700° C.). The conditionnecessary to have such a binary system is that one of the two metals hasa melting point greatly superior to the melting point of the other. Thegold/indium couple (Au—In) represents a typical example.

In practical terms, in the simplest case, a layer of different metal isdeposited on each of the two substrates to be assembled. Then, the twosubstrates are brought into close contact by placing the metallic layersone against the other under pressure. The unit is heated to atemperature slightly greater than the melting point of one of the twometals, for example the indium in the case of the gold/indium couple.The latter melts and wets the surface of the other metal (Au). Then, thesolid-liquid interdiffusion of the two metals generates a consumption ofthe liquid phase (In) and the creation of the solid intermetalliccompositions, firstly AuIn₂ in the case of the gold/indium couple. Itmust be highlighted that the solidifying of the solder joint is carriedout in isothermal conditions inferior to those of the eutectictemperature. This is the point that differentiates the SLID solder fromthe conventional solders where the alloy is made at a temperaturesuperior to its eutectic temperature and the solidifying of the alloy isobtained during cooling. After complete solidification of the solderjoint, the interdiffusion can continue in the solid state until thethermodynamic balance of the system. The ratio of the thicknesses of thelayers deposited is defined by the stoichiometry of the finished alloy.This ratio must be chosen so that the re-melting temperature of thefinished alloy is substantially superior to the temperature of thesoldering process. By way of illustration, in the case of a Au/In systemand a process temperature of 200° C., the ratio of the total thicknessesof the indium and gold layers can be taken as 2 to 1, giving a finalgold/indium alloy composition of 43.1% in weight in indium. Withthermodynamic balance, the final solder of such a system is composed oftwo solid phases AuIn and AuIn₂ marked 12 in FIGS. 5 and 11.

Exempting the Au/In couple, other binary systems can be used for theSLID solder. In order to compose them, a choice can be made, forexample, from couples among the following metals whose list is notrestrictive:

-   -   high melting point: Au, Ag, Pd, Cu;    -   low melting point: In, Sn, Pb.

The SLID solder can also be a ternary alloy, or greater, with theaddition of other elements intended to improve some properties such as,for example, the mechanic properties.

The metallic deposits can be achieved via different vacuum evaporationprocesses or via electroplating. Generally, the thickness of the solderjoint lies between 1 μm and 2 μm.

The heating can be performed via heat or microwave means. In the lattercase, only the conductive layers are heated, thus avoiding the annealingof the active layers of the component and considerably diminishing thetotal time of the assembling process.

As for all metals, indium is Very reactive in the liquid state and couldaggress the metallic mirror and the active layers. The aforementioneddiffusion barrier allows to avoid this aggression. The diffusion barriercould be a layer of titanium, as in the example mentioned above, or alayer of W, Pt, Nb, Cr or Ta, or-even a multilayer or an alloy made ofat least one of these metals.

The assembling technique via SLID solder advantageously allows tosatisfy, among other things, the following three conditions:

-   -   I. a good heat conductivity of the component which ensures an        efficient evacuation of the heat outside the active layers;    -   II. a low temperature process which allows to avoid the        induction of heavy constraints during the cooling, as well as        the healing of the defects created during the irradiation;    -   III. a good surface uniformity of the obtained component.

Once the structures have been assembled, the growth substrate 15 inwhich ions have been implanted and the barrier layer 14 are removed. Thestructure obtained after the removal of the growth substrate and thebarrier layer is represented in FIG. 11.

The removal of the substrate 15 can be done via a mechanical thinningfollowed by a selective etching, dry or wet. The thinning allows toreduce the thickness of the substrate, for example by approximately 90%,and the chemical etching stage allows to remove what remains of thesubstrate. The removal of the substrate 15 can also be entirely done viaselective chemical etching, dry or wet. The selectivity of the etchingprocess must be high (typically greater than 100) so as to protect theremains of the structure. The barrier layer 14 perfectly fulfils thisrole. The barrier layer 14 is composed of material different to that ofthe growth substrate and its thickness is approximately thrice thethickness of the first phase layer.

The removal of the barrier layer 14 is then carried out. An etching, forexample a wet chemical etching, allows to remove the barrier layer. Theselectivity of the etching process must also be high (typically greaterthan 1000) so as to protect the cavity.

A setting of the thickness of the cavity, controlled by a spectralcharacterisation of the component, follows the removal stage of thebarrier layer 14. The purpose of this setting is to make the excitonicabsorption coincide with the mode of cavity resonance. FIG. 12represents setting curves C1, C2 and C3 established during the spectralcharacterisation.

The spectral characterisation firstly allows to localise the spectralposition of the excitonic absorption λ_(e) and the spectral position ofthe mode of cavity resonance λ_(r) (see curve C1). The thickness of thecavity determines the resonance wavelength. The setting is done via avery slow etching of the first phase layer (etching speed for example ofapproximately λ/100 per minute). The etching of the first phase layerallows to off set the mode of cavity resonance so that it coincides withthe excitonic line. The curves C1, C2 and C3 illustrate the developmentof the spectre Of the component during the etching operation. Theadaptation is achieved when the excitonic absoroption coincides with themode of cavity resonance (curve C3). The originality of this stage ofthe process according to the invention resides in the possibility tocontrol the thickness after the growth and after the depositing of themetallic mirror.

The impedance still has to be adapted, that meaning to cancel the totalreflectivity of the component in linear state so as to maximise thecommutation contrast. The impedance adaptation stage is performed viathe depositing of the front mirror 7. The front mirror 7 is a Braggmirror with a reflectivity inferior to the reflectivity of the rearmirror 11. The operating wavelength of the Bragg mirror must obviouslybe centred on that of the excitonic line, so that the mirror does notadd any additional phase delay. This ensures that the cavity resonance,which was regulated on the excitonic resonance, will no longer move. TheBragg mirror can be made via a stacking of dielectric layers, forexample an alternation of SiO₂ and TiO₂ layers or an alternation of SiO₂and Si layers. The front mirror 7 is made via a depositing on the firstphase layer 8. The reflectivity of the front mirror is chosen to respectthe impedance adaptation condition (see equation (1)). The depositing ofthe front mirror leads to the obtaining of the structure according tothe invention represented in FIG. 5. This means of manufacturing whichconsists in carrying out the depositing of the front mirror as the laststage is preferable according to the invention. Indeed, it allows tochoose the adequate deposit (with the reflectivity value which makes theimpedance adaptation condition (1)) in order to cancel the reflectivityof the low intensity component and to thus reinforce its commutationcontrast.

The component according to the invention as well as its method formanufacturing thus have several advantages compared to a component ofthe prior art, advantages among which can be cited:

-   -   the means of manufacturing which allows to control the cavity        parameters (a choice of a front mirror with higher reflectivity        is rendered possible which has the effect of reinforcing the        intra-cavity field and of reducing the saturation power);    -   a low value of the power absorbed by the absorbent material due        to the insignificant thickness of this material (thickness        inferior, for example, to 100 nm);    -   a very good evacuation of the absorbed power due to the fact        that the rear mirror is buried, thanks to the solder joint, in a        very good heat conducting substrate;    -   the fact that the excitonic line is not deteriorated by the        defects created by the ion irradiation;    -   the possibility of controlling the response time of the        component thanks to a prior calibration of the relation between        the response time and the irradiation dosage;    -   the fact that the process does not require the use of a        transparent growth substrate at the operating wavelength as it        is later removed.

By way of illustration, FIG. 13 represents the experimental reflectivitycurves of the component according to the first embodiment of theinvention prior to the depositing of the mirror (curve C4) and after thedepositing of the mirror (curve C5).

A second embodiment of the invention will now be described in referenceto FIGS. 14 to 17.

According to the second embodiment of the invention, the Bragg mirror isan epitaxy semiconductor mirror made during the growth stage ofsemiconductive layers on the aforementioned substrate 15. Thesemiconductive layers which were grown on the substrate 15 are thussuccessively the barrier layer 14, the Bragg mirror 7, the first phaselayer 8, the absorbent structure 9 and the second phase layer 10. TheBragg mirror can then be composed, for example, of an alternation of InPand InGaAsP layers.

FIG. 14 represents a structure obtained following the epitaxial growthstage and FIG. 15 represents the irradiation stage of the thus obtainedstructure.

The irradiation stage follows the depositing stage of the rear mirror 11and of the metallic layer 16 so as to obtain a structure such asrepresented in FIG. 16. The structure as represented in FIG. 16 is thusbrought into contact with the structure as represented in FIG. 9. It isthe layers 16 and 17 which are brought into contact one with the otherso as to form a SLID solder, as this was previously mentioned for thefirst embodiment of the invention. The growth substrate 15 and thebarrier layer 14 are then removed in order to obtain a saturableabsorber component as represented in FIG. 5.

The second embodiment of the invention does not comprise a cavityregulating stage via slow etching of the first phase layer, as is thecase according to the first embodiment.

FIGS. 18 and 19 illustrate experimental results regarding a componentaccording to the invention.

FIG. 18 represents the reflectivity of the component in a logarithmicscale R(Log) according to the energy via pulses E_(pulses) of a pulsestream at 20 MHz at the wavelength of 1.55 μm. A very low reflectivityR_(min) (3%) is noticed for the low levels of incident energy and a highreflectivity R_(max) (40%) for the high levels of incident signal. Thecommutation contrast is estimated at 11 dB with a low saturation energyof 1 pJ.

FIG. 19 represents the standardised non-linear signal of the componentaccording to the delay between the excitation signal and the probesignal. The very fast decline of the signal is the sign of anaccelerated relaxation process thanks to the ion irradiation. Theindicated value (6 ps) is the characteristic time of the exponentialdecline of the signal, obtained for an irradiation Ni⁺ at 11 MeV with adosage of 2.10¹¹ cm⁻².

1-38. (Canceled).
 39. A saturable absorber component comprising: anabsorbent material located between a front mirror and a rear mirror,wherein the rear mirror is a metallic buried mirror fixed by a weldingjoint on a heat conductive substrate, the rear mirror, the weldingjoint, and the heat conductive substrate constituting a set configuredto evacuate power absorbed by the component when a light is incident onthe front mirror.
 40. A component set forth in claim 39, wherein theabsorbent material comprises a set of quantum wells separated by barrierlayers.
 41. A component set forth in claim 40, wherein the quantum wellscomprise InGaAsP wells and the barrier layers comprise InP layers.
 42. Acomponent set forth in claim 40, wherein the absorbent materialcomprises defects created by ion irradiation.
 43. A component set forthin claim 39, wherein the front mirror is a Bragg mirror located on asurface of the component and having a reflectivity inferior to areflectivity of the rear mirror.
 44. A component set forth in claim 43,wherein the Bragg mirror comprises a stack of dielectric layers.
 45. Acomponent set forth in claim 44, wherein the stack of dielectric layerscomprises an alternation of SiO₂ and TiO₂ layers or an alternation ofSiO₂ and Si layers.
 46. A component set forth in claim 43, wherein theBragg mirror is an epitaxy semiconductive Bragg mirror.
 47. A componentset forth in claim 46, wherein the epitaxy semiconductive Bragg mirrorcomprises an alternation of non-absorbent Inp and InGaAsP layers.
 48. Acomponent set forth in claim 47, wherein the InGaAsP layers aretransparent at an operating wavelength.
 49. A component set forth inclaim 39, further comprising: a first phase control layer locatedbetween the front mirror and the absorbent material; and a second phasecontrol layer located between the absorbent material and the rearmirror.
 50. A component set forth in claim 49, wherein the first andsecond phase control layers comprise InP layers.
 51. A component setforth in claim 39, further comprising: a diffusion barrier between therear mirror and the welding joint.
 52. A component set forth in claim51, wherein the diffusion barrier comprises a layer, or a multilayer, oran alloy made from at least one of the metals chosen from Ti, W, Pt, Nb,Cr or Ta.
 53. A component set forth in claim 39, wherein the weldingjoint comprises an intermetallic alloy.
 54. A component set forth inclaim 53, wherein the intermetallic alloy comprises at least one elementchosen among the following materials: Au, Ag, Cu, Pd and at least oneelement chosen among the following elements: In, Sn, Pb.
 55. A componentset forth in claim 39, wherein the rear mirror is in Au or Ag.
 56. Amanufacturing method of saturable absorber components including anabsorbent material located between a front mirror and a rear mirror, themethod comprising: creating a first structure by depositing a firstmetallic layer on a heat conductive substrate; creating a secondstructure comprising, on a growth substrate, the absorbent material anda second metallic layer; bringing the first and second metallic layersinto contact; and solid-liquid interdiffusion soldering the first andsecond metallic layers.
 57. A method set forth in claim 56, wherein thecreating the second structure comprises stacking, on the growthsubstrate, a barrier layer, a first phase layer, the absorbent material,a second phase layer, the rear mirror, and the second metallic layer.58. A method set forth in claim 57, further comprising, before thestacking of the rear mirror on the second phase layer, an ionirradiation of the second phase layer to create crystalline defects inthe absorbent material.
 59. A method set forth in claim 57, wherein thecreating the second structure further comprises depositing a diffusionbarrier on the rear mirror and depositing a layer of gold on thediffusion barrier.
 60. A method of saturable absorber components setforth in claim 56, further comprising, successively, removing the growthsubstrate and removing the barrier layer and, after removing the barrierlayer, slow etching the first phase layer, said slow etching beingcontrolled by a spectral characterisation of the component.
 61. A methodset forth in claim 60, further comprising, after the slow etching,depositing the front mirror.
 62. A method set forth in claim 61, whereinthe front mirror is a Bragg mirror made by stacking dielectric layers.63. A method set forth in claim 62, wherein the stacking dielectriclayers comprises an alternation of SiO₂ and TiO₂ layers or of analternation of SiO₂ and Si layers.
 64. A method set forth in claim 56,wherein the creating the second structure comprises epitaxial growth, onthe growth substrate, successively, a barrier layer, a front mirror, afirst phase layer, the absorbent material, a second phase layer, therear mirror, and the second metallic layer.
 65. A method set forth inclaim 64, further comprising, before the epitaxial growth of the rearmirror on the second phase layer, an ion irradiation of the second phaselayer to create crystalline defects in the absorbent material.
 66. Amethod set forth in claim 58, wherein irradiation energy in the ionirradiation is adjusted so that ions end their travel in the growthsubstrate.
 67. A method set forth in claim 58, wherein the ions are Ni⁺⁶ions.
 68. A method set forth in claim 64, wherein the creating thesecond structure further comprises depositing a diffusion barrier on therear mirror and depositing a layer of gold on the diffusion barrier. 69.A method set forth in claim 64, wherein the front mirror is a Braggmirror made by an alternation of Inp and InGaAsP layers.
 70. A methodset forth in claim 64, further comprising, successively, removing thegrowth substrate and removing the barrier layer.
 71. A method set forthin claim 60, wherein the removing the growth substrate comprisesmechanical polishing and then etching.
 72. A method set forth in claim60, wherein the removing the barrier layer comprises etching.
 73. Amethod set forth in claim 56, wherein the depositing the first metalliclayer is preceded by depositing a bonding layer on the heat conductivesubstrate.
 74. A method set forth in claim 56, wherein the firstmetallic layer is made from at least one of the following metals: Au,Ag, Pd, Cu and in that the second metallic layer is made from any one ofthe following metals: In, Sn, Pb.
 75. A method set forth in claim 56,wherein the depositing the absorbent material comprises depositing asuccession of quantum wells and barriers separating the quantum wells.76. A method set forth in claim 56, further comprising depositing therear mirror in a form of a gold or silver layer deposit.